Convert String Into Date Format 'YYYY/MM/DD'?

I have an issue as mentioned below.
My source is File (.txt) has string data type which have dates like '20130731'. And I need to convert the data into below mentioned format and I have to load to target which have Date data type.

" YYYY/MM/DD". I am not able to get the exact data, and I've gone through Informatica help. It is saying to_date(to_char(string,format),'YYYY/MM/DD') ---> the format should be same as passing string.
Please advise what to do?
Thanks in Advance

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